Handover for an intermediate node in a wireless communication network

ABSTRACT

The disclosure relates to an intermediate node arranged to relay information between a donor node and at least one served node, and comprises a served antenna arrangement that communicates by means of at least a first and second electrically steerable antenna radiation lobe. During a first mode of operation, all antenna radiation lobes are directed towards a first donor node. During a second mode of operation, the antenna radiation lobes are directed such that the intermediate node is in contact with both the first donor node and the second donor node. During a third mode of operation, all antenna radiation lobes are directed towards the second donor node. A first polarization is associated with each lobe directed towards the second donor node during the second mode of operation and a second polarization is associated with each lobe directed towards the first donor node during the second mode of operation.

This application claims the benefit of U.S. Provisional PatentApplication No. 61/550,121, filed on Oct. 21, 2011. The entirety of saidapplication is incorporated by reference herein.

TECHNICAL FIELD

The present invention relates to an intermediate node in a wirelesscommunication network. The intermediate node is arranged to relayinformation between a donor node and at least one served node, andcomprises a served antenna arrangement that is adapted to communicatewith each donor node by means of at least a first antenna radiation lobeand a second antenna radiation lobe. The antenna radiation lobes areelectrically steerable such that during a first mode of operation, theserved antenna arrangement is adapted to direct all antenna radiationlobes towards a first donor node. Furthermore, during a second mode ofoperation, following the first mode of operation, when the first donornode has been determined to be exchanged with a second donor node bymeans of handover, the served antenna arrangement is adapted to directat least the first antenna radiation lobe towards the second donor node.Then the served antenna arrangement is also adapted to maintain at leastthe second antenna radiation lobe directed towards the first donor nodesuch that, during the second mode of operation, the intermediate node isin contact with both the first donor node and the second donor nodeduring hand-over procedures for the first donor node and the seconddonor node. Finally, during a third mode of operation, corresponding tothe first mode of operation, the served antenna arrangement is adaptedto direct all antenna radiation lobes towards the second donor node.

The present invention also relates to a method for changing a firstdonor node to a second donor node for an intermediate node in a wirelesscommunication network. The intermediate node is used to relayinformation between donor nodes and at least one served node, theintermediate node communicating with each donor node by means of atleast a first antenna radiation lobe and a second antenna radiationlobe. The antenna radiation lobes are electrically steerable. The methodcomprises the steps: (a) during a first mode of operation, directing allantenna radiation towards a first donor node; (b) during a second modeof operation, following the first mode of operation, when the firstdonor node is going to be exchanged with a second donor node by means ofhandover, directing at least the first antenna radiation lobe towardsthe second donor node. This step also comprises maintaining at least thesecond antenna radiation lobe directed towards the first donor node,such that, during the second mode of operation, the intermediate node isin contact with both the first donor node and the second donor nodeduring handover procedures for the first donor node and the second donornode; and (c) during a third mode of operation, corresponding to thefirst mode of operation, directing all antenna radiation lobes towardsthe second donor node.

BACKGROUND

Repeaters and relays are efficient for both providing coverage in areaswithout coverage and also to provide increased data rates to areas withweak signal strength for example at cell edge and indoor. A repeaterworks in the physical layer and amplifies and forwards the signal,including present noise and interference. A relay typically decodes thedata before amplifying and forwarding the signal, which means thatinterference and noise will not be forwarded.

Repeaters and relays are usually served by a base station called donorbase station, and usually serve user terminals. If the antenna at therepeater or relay intended for communication with the donor base stationis reconfigurable, for example by means of beam-forming, the donor basestation could be changed by pointing the beam of the reconfigurableantenna from the current donor base station to another base station. Thereason for doing this could for example be that the current donor basestation is overloaded or breaks down.

Repeaters and relays that are placed on moving objects like for exampletrains or ships are called mobile relays. A mobile relays must changedonor base station due to that the train and ships will move from onecell to another.

When using a reconfigurable antenna at repeaters or relays for changingthe donor base station, some kind of handover is required. For arepeater, all the user terminals served by that repeater must make ahandover from the current donor base station to the new donor basestation. If the change of donor base station becomes too quick, all theuser terminals will not have time required to do these handovers andconnections will be dropped. For a relay, the user terminals that areserved by that relay do not have to make handovers due to that they areconnected to the relay regardless of which donor base station the relaygot. That is, the donor base station is transparent to the userterminals since the relay acts like a base station. However, the relayitself has to make a handover from the current donor base station to thenew donor base station.

US 2006229076 discloses a wireless communication terminal on a mobileplatform, such as a train, that makes use of directional antennas ableto accomplish soft handoffs between base transceiver stations. Anantenna controller controls a beam-forming network to generate a firstand a second lobe, the first lobe being directed towards a donor basestation and the second lobe being used to continuously scan for one ormore different base transceiver stations sites that may be available toform a higher quality link.

However, it is difficult to maintain coverage for the first lobe whilehaving a desired flexibility with the second lobe. Furthermore, if thesecond lobe suddenly finds a different base transceiver station, therewill be a lot of interference in the radio.

It is therefore a desire to provide a repeater or a relay with animproved handover when changing donor base station for relay andrepeater compared with prior art.

SUMMARY

It is an object of the present invention to provide a repeater or arelay with an improved handover when changing donor base station forrelay and repeater compared with prior art.

Said object is obtained by means of an intermediate node in a wirelesscommunication network. The intermediate node is arranged to relayinformation between a donor node and at least one served node, andcomprises a served antenna arrangement that is adapted to communicatewith each donor node by means of at least a first antenna radiation lobeand a second antenna radiation lobe. The antenna radiation lobes areelectrically steerable such that during a first mode of operation, theserved antenna arrangement is adapted to direct all antenna radiationlobes towards a first donor node. Furthermore, during a second mode ofoperation, following the first mode of operation, when the first donornode has been determined to be exchanged with a second donor node bymeans of handover, the served antenna arrangement is adapted to directat least the first antenna radiation lobe towards the second donor node.Then the served antenna arrangement is also adapted to maintain at leastthe second antenna radiation lobe directed towards the first donor nodesuch that, during the second mode of operation, the intermediate node isin contact with both the first donor node and the second donor nodeduring hand-over procedures for the first donor node and the seconddonor node. Finally, during a third mode of operation, corresponding tothe first mode of operation, the served antenna arrangement is adaptedto direct all antenna radiation lobes towards the second donor node.Furthermore, the served antenna arrangement is arranged to communicateby means of a first polarization and a second polarization. The firstpolarization is associated with each antenna radiation lobe directedtowards the second donor node during the second mode of operation andthe second polarization is associated with each antenna radiation lobedirected towards the first donor node during the second mode ofoperation.

Said object is obtained by means of a method for changing a first donornode to a second donor node for an intermediate node in a wirelesscommunication network. The intermediate node is used to relayinformation between donor nodes and at least one served node, theintermediate node communicating with each donor node by means of atleast a first antenna radiation lobe and a second antenna radiationlobe. The antenna radiation lobes are electrically steerable. The methodcomprises the steps: (a) during a first mode of operation, directing allantenna radiation towards a first donor node; (b) during a second modeof operation, following the first mode of operation, when the firstdonor node is going to be exchanged with a second donor node by means ofhandover, directing at least the first antenna radiation lobe towardsthe second donor node. This step also comprises maintaining at least thesecond antenna radiation lobe directed towards the first donor node,such that, during the second mode of operation, the intermediate node isin contact with both the first donor node and the second donor nodeduring handover procedures for the first donor node and the second donornode; and (c) during a third mode of operation, corresponding to thefirst mode of operation, directing all antenna radiation lobes towardsthe second donor node.

Furthermore, the method also comprises the step of communicating bymeans of a first polarization and a second polarization. The firstpolarization is associated with each antenna radiation lobe directedtowards the second donor node during the second mode of operation andthe second polarization is associated with each antenna radiation lobedirected towards the first donor node during the second mode ofoperation.

According to an example, the intermediate node is a repeater or a relay.

According to another example, the served node is constituted by at leastone user terminal.

According to another example, the intermediate node is arranged toevaluate whether there is a suitable second donor node. When performingsaid evaluation, the intermediate node may take antenna gains intoaccount.

Other examples are disclosed in the dependent claims.

The main advantage of the invention is that handovers could more easilybe made when changing donor base station for an intermediate node suchas a relay or a repeater. This will lead to fewer dropped calls anddisconnections. It also enables load sharing actions where anintermediate node is enforced to change donor base station. Bymaintaining the received signal strength of both a serving donor nodeand a candidate donor node within a threshold for a sufficiently longtime, it is possible to have time to complete all handovers of all userterminals served by the intermediate node. This means that the userterminals have time to perform a correct and complete handover.

Furthermore, in case of the intermediate node being constituted by arelay, the prolonged handover time enables the more complicated relayhandover to be completed satisfactory. The prolonged handover time isalso helpful for idle user terminals reselecting cells during thesehandover times.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described more in detail withreference to the appended drawings, where:

FIG. 1 schematically shows a repeater/relay mounted to a building in afirst mode of operation.

FIG. 2 schematically shows a repeater/relay mounted to a building in atthe start of a second mode of operation.

FIG. 3 schematically shows a repeater/relay mounted to a building in asecond mode of operation.

FIG. 4 schematically shows a repeater/relay mounted to a building in athird mode of operation.

FIG. 5 schematically shows a repeater/relay mounted to a moving train ina first mode of operation.

FIG. 6 schematically shows a repeater/relay mounted to a moving train ina second mode of operation.

FIG. 7 schematically shows a repeater/relay mounted to a moving train ina third mode of operation.

FIG. 8 schematically shows a flow chart of a method according to thepresent invention.

DETAILED DESCRIPTION

The third generation partnership project (3GPP) is currently working onstandardization of the Long Term Evolution (LTE) concept. LTE can beused as an exemplifying radio access technology. However, theseembodiments are essentially equally applicable to other radio accesstechnologies as well.

In the following, since the description will be directed to a repeateror a relay, the term intermediate node will be used for these or similardevices. Furthermore, handover procedures for different radio accesstechnologies are regarded as commonly known, and their details will notbe further discussed here.

With reference to FIG. 1, showing a first example, there is a building17 at which there is an intermediate node 1 which is comprised in awireless communication network 2. The intermediate node 1 is arranged torelay information between a first donor node 3 and four served nodes inthe form of user terminals 5, 6, 7, 8 in the building 17. The firstdonor node 3 then functions as a serving donor node.

The intermediate node 1 comprises a served antenna arrangement 9 that isadapted to communicate with the first donor node 3 by means of a firstantenna radiation lobe 10 and a second antenna radiation lobe 11, wherethe antenna radiation lobes 10, 11 are electrically steerable. Theserved antenna arrangement 9 is for example constituted by areconfigurable antenna.

The intermediate node further comprises a serving antenna arrangement 18which is used for communication between the intermediate node 1 and theuser terminals 5, 6, 7, 8. The serving antenna arrangement 18 may be ofany suitable type, either having one or more fixed and/or steerableantenna radiation lobes.

During a first mode of operation, as shown in FIG. 1, the served antennaarrangement 9 is adapted to direct the antenna radiation lobes 10, 11 ofthe served antenna arrangement 9 towards the first donor node 3, suchthat communication between the intermediate node 1 and the first donornode 3 takes place by means of both antenna radiation lobes 10, 11.

During a second mode of operation, following the first mode ofoperation, the first donor node 3 has been determined to be exchangedwith a second donor node 4 by means of handover. Then, as shown in FIG.2 and FIG. 3, the served antenna arrangement 9 is adapted to direct thefirst antenna radiation lobe 10 towards the second donor node 4 and tomaintain the second antenna radiation lobe 11 directed towards the firstdonor node 3. In this way, during the second mode of operation, theintermediate node 1 is in contact with both the first donor node 3 andthe second donor node 4 during hand-over procedures for the first donornode 3 and the second donor node 4. The wireless communication network 2performs the hand-over procedures in a previously known way which isdepending on which radio system that is used, where the hand-over isfacilitated by means of the intermediate node 1 being in contact withboth the first donor node 3 and the second donor node 4 during hand-overprocedures.

In the case of the intermediate node 1 being constituted by a relay, thehand-over from one donor node to the next donor node for the relay isfacilitated, and in the case of the intermediate node 1 beingconstituted by a repeater, the hand-over from one donor node to the nextdonor node for the user terminals 5, 6, 7, 8 is facilitated.

During a third mode of operation, as shown in FIG. 4, the served antennaarrangement 9 is adapted to direct both antenna radiation lobes 10, 11towards the second donor node. Here, the hand-over procedures haveterminated, the third mode of operation corresponding to the first modeof operation.

The donor nodes 3, 4 may be in the form of base stations, where thefirst donor node is constituted by a serving base station in the firstmode of operation, and the second donor node is constituted by acandidate base station which in the third mode of operation, afterhandover completion, has been converted into a serving base station. Theserving base station is positioned in a serving cell, and the candidatebase station is positioned in a candidate cell.

According to the present invention, the served antenna arrangement 9 isarranged for communicating by means of a first polarization P1 and asecond polarization P2. The first polarization P1 is associated with thefirst antenna radiation lobe 10, and the second polarization P2 isassociated with the second antenna radiation lobe 11.

In the following, a more detailed version of the first example will bedescribed. According to this version, the intermediate node 1 isconstituted by an outdoor-to-indoor repeater with a reconfigurableantenna 9, and the first donor node 3 is constituted by a first donorbase station, which at this stage is the current donor base station forthe repeater 1. For example, the first donor base station 3 isoverloaded due to too much traffic, and it would be better for therepeater 1 to change donor base station to the second donor node 4 whichis constituted by a second donor base station 4, and which at this stageis constituted by a chosen candidate base station.

If the antenna radiation lobes 10, 11 of both polarizations of thereconfigurable antenna 9 at the repeater 1 instantly would be directedtowards the second donor node 4, the user terminals 5, 6, 7, 8 served bythe repeater 1 would not have enough time to do handovers from the firstdonor base station 3 to the second donor base station, 4 and calls wouldbe dropped.

Instead, first the first antenna radiation lobe 10 of the firstpolarization P1 of the reconfigurable antenna 9 is be directed towardsthe second donor base station 4, as shown in FIG. 2 and FIG. 3. Then itis possible for the user terminals 5, 6, 7, 8 served by the repeater 1to do handovers from the first donor base station 3 to the second donorbase station 4. However, the user terminals 5, 6, 7, 8 will typicallyconnect to the base station that gives the user terminals 5, 6, 7, 8 thebest signals; therefore it might be necessary to reduce the power of thefirst antenna radiation lobe 10, as can be seen in FIG. 3.

It is also possible that the first donor base station 3, when theantenna reconfiguration is completed, initiates the handover proceduretowards the user terminals 5, 6, 7, 8. When the user terminals 5, 6, 7,8 have made their handovers from the first donor base station 3 to thesecond donor base station 4, also the second antenna radiation lobe 11of the second polarization P2 of the reconfigurable antenna 9 isdirected towards the second donor base station 4 as can be seen in FIG.4.

In a second example, with reference to FIG. 5, an intermediate node 1′is arranged at a train 12 and is comprised in a wireless communicationnetwork 2′. The intermediate node 1′ is arranged to relay informationbetween a first donor node 3′ and at four served nodes in the form ofuser terminals in the train (not shown).

The intermediate node 1 is adapted to communicate with the first donornode 3′ by means of a first antenna radiation lobe 10′ and a secondantenna radiation lobe 11′, where the antenna radiation lobes 10′, 11′are electrically steerable in the same way as in the first example. Forthis purpose, the intermediate node 1′ has a not shown antennaarrangement similar to the one in the first example.

A corresponding first mode of operation, second mode of operation andthird mode of operation are shown in FIG. 5, FIG. 6 and FIG. 7, as thetrain 12 travels in a direction D along its track and the first donornode 3′ is exchanged with a second donor node 4′ by means of handover.

In accordance with the present invention, also in this example, theintermediate node 1′ is arranged for communicating by means of a firstpolarization P1′ and a second polarization P2′. The first polarizationP1′ is associated with the first antenna radiation lobe 10′, and thesecond polarization P2′ is associated with the second antenna radiationlobe 11′.

For example, more in detail, the intermediate node 1 may here beconstituted by a mobile relay 1′ with dual polarized reconfigurableantennas, the mobile relay 1′ being placed on the train 12. In FIG. 5,the antenna radiation lobes 10′, 11′ are pointing at the first donornode 3′ due to that the mobile relay 1′ is closest to this node whichmay be constituted by a base station. As the train 12 moves along therailway in the direction D, the distance to the first donor node 3′becomes larger, and the distance to the second donor node 4′ becomesshorter.

In FIG. 6, the mobile relay 1′ has about the same distance to the firstdonor node 3′ and the second donor node 4′. Now, the mobile relay 1′starts the process of changing donor base station. If the antennaradiation lobes 10′, 11′ of both polarizations would be re-directed fromthe first donor node 3′ to the second donor node 4′ at the same time,the handover for the relay from the first donor node 3′ to the seconddonor node 4′ would be difficult. Therefore, the first antenna radiationlobe 10′ is first re-directed as shown in FIG. 6. Now a handover for themobile relay 1′ from the first donor node 3′ to the second donor node 4′can be made. When the handover is made, also the antenna radiation lobe10′ is re-directed from the first donor node 3′ to the second donor node4′.

As disclosed in the two examples above, the antenna radiation lobes 10,11; 10′, 11′ may be directed independent of each other, and interferencebetween the two antenna radiation lobes 10, 11; 10′, 11′ is reducedsince different polarizations and possibly different radio chains may beused.

Generally, the basic concept of the invention is to make a smooth changeof donor nodes such as donor base stations for repeaters and relays byusing a reconfigurable antenna 9 at the intermediate node 1, 1′. Thesmooth change could be made by first re-directing the beam of the firstpolarization P1, P1′ from the current donor base station 3, 3′ towardsthe new donor base station 4, 4′. Then the intermediate node 1, 1′ has agood connection with both base stations 3, 3′; 4, 4′ and thereforehandovers could be made. After the handovers are made, the beam of thesecond polarization P2, P2′ is also re-directed from the current donorbase station 3, 3′ to the new donor base station 4, 4′.

The handover indication can be determined by the current donor basestation in the current cell, or by intermediate node 1, 1′ itself.

The intermediate node 1, 1′ may regularly use the first antennaradiation lobe 10, 10′ to search for candidate base stations incandidate cells in order to evaluate whether there is a suitable seconddonor node. The search can either be made by finding an optimal beamformer considering the direction to candidate cells, or by evaluating anumber of alternative antenna radiation lobes. The intermediate node 1,1′ is considered ready for handover when a candidate cell constitutes arelevant cell with adequate radio conditions including the antennagains. Antenna gains may include such features as the possibility ofbeamforming. This may be performed in several different ways: (A) basedon localization of the intermediate node 1, 1′, also benefitting fromrepetitive behavior. At a specific estimated location, the intermediatenode 1, 1′ acquires an indication that a handover is possible andinitiates an alternative antenna radiation lobe evaluation. Thelocalization could either be based on GPS (Global Positioning System),or on RF (Radio Frequency) fingerprinting; a combination of detectedcells indicate a crude position estimate; (B) based on past handoverfailure and radio link failure statistics in the donor base station 3,3′ or intermediate node 1, 1′ for specific cell transitions, typicallyfor the repetitive behavior of trains, buses etc. If a past handoverindication was considered too late to enable all user terminals 5, 6, 7,8 to complete the handover and causing handover failures, then thehandover is indicated more early the next time being served by the samecell; (C) based on information about handover statistics and possiblyalso localization from prior handovers but by othertrains/buses/vehicles. Such information can be aggregated and conveyedto the intermediate node 1, 1′ by the donor base station 3, 3′, otherradio access nodes such as an RNC (Radio Network Controller), a corenetwork node, or an operation and maintenance node.

The intermediate node 1, 1′ is thus arranged to include statisticsregarding past changes of donor node when performing said evaluation.For example, a first vehicle and a second vehicle may pass the donornodes A, B, C and D in this order, the first vehicle passing the donornodes before the second vehicle. When considering the transition fromdonor node C to donor node D for the second vehicle when the firstvehicle has passed all the donor nodes A, B, C and D, there are two mainalternatives for said past changes: (A) taking the transition betweendonor node C and D for the first vehicle into account; (B) taking thetransition between donor node B and C for the second vehicle intoaccount.

Alternative (1) above is the one of main interest, but of coursealternative (2) may be of interest as well, since previous handovers fora certain vehicle also comprises information. A combination of thesealternatives is of course also conceivable.

Furthermore, other alternatives may include earlier transitions for bothvehicles, for example the transition between donor node B and C for thefirst vehicle and the transition between donor node A and B for thefirst vehicle, even if these alternatives probably comprises less usefulinformation the first two alternatives above.

The reconfigurable antenna 9 is configured to enable long enoughhandover transition time in order to complete a group handover. The timefrom a handover indication to a handover complete indication can be oneout of, or a combination of the following (A)-(E):

(A) Pre-determined time, based on handover time information. Thehandover time information could be determined in the donor base station3, 3′ and signaled to the intermediate node 1, 1′ or be determined inthe intermediate node 1, 1′ itself.

(B) Based on train velocity, possibly estimated by the intermediate node1, 1′ using dedicated sensor and circuitry, or estimated from the rateof variation in the wireless radio channel, e.g. via Doppler shift orDoppler spread estimates.

(C) Based on past handover failure statistics and radio link failure inthe donor base station or intermediate node 1, 1′ for specific celltransitions, typically for the repetitive behavior of trains, buses etc.If a past handover time was considered too short to enable all userterminals 5, 6, 7, 8 to complete the handover and causing handoverfailures, then the handover time is prolonged the next time passing thesame cell to cell crossing.

(D) Based on localization of the intermediate node 1, 1′, alsobenefitting from repetitive behavior. At a specific estimated location,the intermediate node 1, 1′ discloses a handover complete indication.The localization could either be based on GPS, or on RF fingerprinting;a combination of detected cells indicate a crude position estimate.

(E) Based on information about handover statistics and possibly alsolocalization from prior handovers but by other trains/buses/vehicles.Such information can be aggregated and conveyed to the intermediate node1, 1′ by the donor base station, other radio access node such as an RNC,a core network node, or an operation and maintenance node.

The respective antenna radiation lobes for the served antennaarrangement 9 can for example be generated by monitoring the downlinkdirection of the serving, donor, base stations and candidate basestations with help of for example DOA estimation. Antenna radiationlobes targeting candidate base stations could also be selected from anumber of fixed antenna radiation lobes, each regularly evaluated.

The antenna radiation lobes can also be generated based on informationabout handover statistics, generated antenna radiation lobes andpossibly also localization from prior handovers, but by othertrains/buses/vehicles. Such information can be aggregated and conveyedto the intermediate node 1, 1′ by the donor base station, other radioaccess node such as an RNC, a core network node, or an operation andmaintenance node.

With reference to FIG. 8, the present invention also relates to a methodfor changing a first donor node 3, 3′ to a second donor node 4, 4′ foran intermediate node 1, 1′ in a wireless communication network 2, 2′.The intermediate node 1, 1′ is used to relay information between donornodes 3, 4; 3′, 4′ and at least one served node 5, 6, 7, 8. Theintermediate node 1, 1′ communicates with each donor node 3, 4; 3′, 4′by means of at least a first antenna radiation lobe 10, 10′ and a secondantenna radiation lobe 11, 11′, the antenna radiation lobes 10, 11; 10′,11′ being electrically steerable. The method comprises the steps: (13)during a first mode of operation, directing all antenna radiation lobes(10μ, 11; 10′, 11′ towards a first donor node 3, 3′; (14) during asecond mode of operation, following the first mode of operation, whenthe first donor node 3, 3′ is going to be exchanged with a second donornode 4, 4′ by means of handover, directing at least the first antennaradiation lobe 10, 10′ towards the second donor node 4, 4′ andmaintaining at least the second antenna radiation lobe 11, 11′ directedtowards the first donor node 3′, such that, during the second mode ofoperation, the intermediate node 1, 1′ is in contact with both the firstdonor node 3, 3 and the second donor node 4, 4′ during handoverprocedures for the first donor node 3, 3′ and the second donor node 4,4′, and (15) during a third mode of operation, corresponding to thefirst mode of operation, directing all antenna radiation lobes 10, 11;10′, 11′ towards the second donor node 4, 4′.

The method further comprises the step of: (16) communicating by means ofa first polarization P1 and a second polarization P2, the firstpolarization being associated with each antenna radiation lobe 10, 10′directed towards the second donor node 4, 4′ during the second mode ofoperation and the second polarization P2 being associated with eachantenna radiation lobe 11, 11′ directed towards the first donor node 3,3′ during the second mode of operation.

The present invention is not limited to the above, but may vary freelywithin the scope of the appended claims. For example, the antennaradiation lobes 10, 11; 10′, 11′ may be electrically steerable by meansof either analogue control or digital control.

Furthermore, the number of antenna radiation lobes may vary, but thereis at least two antenna radiation lobes, where, generally, during thefirst mode of operation, the served antenna arrangement 9 is adapted todirect all antenna radiation lobes 10, 11; 10′, 11′ towards a firstdonor node 3, 3′, and where, during the second mode of operation, theserved antenna arrangement 9 is adapted to direct at least the firstantenna radiation lobe 10, 10′ towards the second donor node 4, 4′ andto maintain at least the second antenna radiation lobe 11, 11′ directedtowards the first donor node 3, 3′. Furthermore, during the third modeof operation, the served antenna arrangement 9 is adapted to direct allantenna radiation lobes 10, 11; 10′, 11′ towards the second donor node4, 4′.

The first polarization P1 is thus associated with each antenna radiationlobe 10, 10′ directed towards the second donor node 4, 4′ during thesecond mode of operation, and the second polarization P2 is associatedwith each antenna radiation lobe 11, 11′ directed towards the firstdonor node 3, 3′ during the second mode of operation.

The polarizations have mutually separate directions, and are for examplemutually orthogonal. The term orthogonal is not to be interpreted as amathematical exact term, but to be within the limits of what ispractically obtainable.

As an auxiliary example, not being comprised in the present claims,instead of re-directing the pointing directions of the antenna radiationlobes, it is instead conceivable that the polarizations of the antennaradiation lobes are changed, possibly in combination with re-directionof the pointing direction. Thus certain antenna radiation lobecharacteristics may be directed towards the donor nodes during thedifferent modes of operation described previously, where those antennaradiation lobe characteristics may be antenna radiation lobe pointingdirection and/or antenna radiation lobe polarization.

The invention claimed is:
 1. An intermediate node in a wirelesscommunication network, the intermediate node being arranged to relayinformation between a donor node and at least one served node, theintermediate node comprising: a served antenna arrangement that isadapted to communicate with each donor node by means of at least a firstantenna radiation lobe and a second antenna radiation lobe, wherein theantenna radiation lobes are electrically steerable and the intermediatenode is configured such that: (a) during a first mode of operation, theserved antenna arrangement is adapted to direct the first and secondantenna radiation lobes towards a first donor node, (b) during a secondmode of operation, following the first mode of operation, when the firstdonor node has been determined to be exchanged with a second donor nodeby means of handover, the served antenna arrangement is adapted todirect at least the first antenna radiation lobe towards the seconddonor node and to maintain at least the second antenna radiation lobedirected towards the first donor node such that, during the second modeof operation, the intermediate node is in contact with both the firstdonor node and the second donor node during hand-over procedures for thefirst donor node and the second donor node, and (c) during a third modeof operation, corresponding to the first mode of operation, the servedantenna arrangement is adapted to direct the first and second antennaradiation lobes towards the second donor node, and the served antennaarrangement is arranged to communicate by means of a first polarizationand a second polarization, the first polarization being associated witheach antenna radiation lobe directed towards the second donor nodeduring the second mode of operation and the second polarization beingassociated with each antenna radiation lobe directed towards the firstdonor node during the second mode of operation.
 2. The intermediate nodeaccording to claim 1, wherein the antenna radiation lobes areelectrically steerable by means of either analogue control or digitalcontrol.
 3. The intermediate node according to claim 1, wherein theintermediate node is a repeater or a relay.
 4. The intermediate nodeaccording to claim 1, wherein said served node comprises a userterminal.
 5. The intermediate node according to claim 1, wherein theintermediate node is arranged to evaluate whether there is a suitablesecond donor node.
 6. The intermediate node according to claim 5,wherein the intermediate node is arranged to take antenna gains intoaccount when performing said evaluation.
 7. The intermediate nodeaccording to claim 6, wherein the intermediate node is arranged toinclude statistics regarding past changes of donor node when performingsaid evaluation.
 8. The intermediate node according to claim 1, whereinthe intermediate node is positioned either at a vehicle, or in vehicle.9. A method for changing a first donor node to a second donor node foran intermediate node in a wireless communication network, theintermediate node being used to relay information between donor nodesand at least one served node, the intermediate node communicating witheach donor node by means of at least a first antenna radiation lobe anda second antenna radiation lobe, the antenna radiation lobes beingelectrically steerable, the method comprising: during a first mode ofoperation, directing the first and second antenna radiation lobestowards a first donor node; during a second mode of operation, followingthe first mode of operation, when the first donor node is going to beexchanged with a second donor node by means of handover, directing atleast the first antenna radiation lobe towards the second donor node andmaintaining at least the second antenna radiation lobe directed towardsthe first donor node, such that, during the second mode of operation,the intermediate node is in contact with both the first donor node andthe second donor node during handover procedures for the first donornode and the second donor node; during a third mode of operation,following the second mode of operation, directing the first and secondantenna radiation lobes towards the second donor node; and communicatingby means of a first polarization and a second polarization, the firstpolarization being associated with each antenna radiation lobe directedtowards the second donor node during the second mode of operation andthe second polarization being associated with each antenna radiationlobe directed towards the first donor node during the second mode ofoperation.
 10. The method according to claim 9, wherein the intermediatenode is used for evaluating whether there is a suitable second donornode.
 11. The method according to claim 10, wherein the intermediatenode uses antenna gains when performing said evaluation.
 12. The methodaccording to claim 10, wherein the intermediate node uses statisticsregarding past changes of donor node when performing said evaluation.13. The method according to claim 9, wherein the intermediate node isused either at a vehicle, or in vehicle.